Wednesday, July 30, 2008

How complete is Open Street Map?

OSM is a great project and as it gains in coverage it becomes an increasingly attractive proposition. One of my former clients in Local Government was excitedly talking about the potential to use OSM for some of their partnership projects, which prompted me to look at OSM in a little more detail.

Take a look at these two similar scale images of Highgate, North London from OSM and Google.



The OSM version has some footpaths and also includes the railway line which Google does not show, plus in my opinion the cartography in OSM is the nicest I have seen of any web maps (I know that is not their raison d'etre but it is still nice). Unfortunately when you look a bit more carefully you will see that there are some small streets missing and some of the road name attribution is different to the TeleAtlas data in Google. I have highlighted a few differences below but have not searched for all.

In Google

and in OSM
Now OSM is a community project and I don't think they make any claims about completeness or accuracy of attribution. However those of us in the GeoCommunity who consider using OSM in a project or who promote the development of crowd sourced data need to be aware of its potential limitations. Unfortunately at the moment there is no way that I can see to guage the level of completeness of OSM which seems to make it a bit of a lottery.

At AGI GeoCommunity08 there are a couple of potentially very interesting sessions on on this topic from Andy Coote and Nick Black


Paul G said...

OSM is a great project and already an attractive proposition for many. I agree we should know what we are getting into before we commit ourselves. When looking at OSM and Google in a little more detail I found the position to be reversed in respect of missing streets for my area of interest. Do take a look at the two links comparing OSM and Google:

With regard to completeness the following page contains information relating to OSM mapping activity that is specific to the United Kingdom
OSM Mapping Activity

I’m sure the sessions from Andy Coote and Nick Black at AGI GeoCommunity08 are worthy of support.

SteveC said...

So did you go and find out if it was correct and fix any mistakes?

Steven said...


If you bring in the aerial imagery in Google or evn better Maps Live (Microsoft)you will see that the extra roads that OSM is showing in the comparison you have posted were under construction the last time the imagery was flown. I imagine (knowing this area a little) tht TeleAtlas and Navteq have not yet got round to capturing these new developments.

I guess there are one or two keen OpenStreetMappers in your area who are doing an excellent job and are in front of the commercial providers. Unfortunately that is not true of Highgate or some other areas. see my follow-up post for some more detail.

Steve C - I will try to update (even though interface is not very friendly) but that was not the point of my post.


Matt said...

Not directly comparable to your example, but I've noticed in rural areas that Google maps shows tracks which are in fact private farm tracks or drives, and not adopted streets or public rights of way.

It may therefore be the case that OSM is in fact providing a more accurate picture of what's public, but as you say, the problem is that you can't know how accurate or complete its picture is.

sexy11 said...